This investigation will elucidate the structural behavior of the normal human acetabulum and examine the alterations in acetabular mechanics after total hip replacement surface replacement, and femoral endoprosthesis hip arthroplasty. The project will involve direct mechanical testing of cadaver specimens and the generation of 2-D and 3-D finite element models for numerical stress analysis. As in vitro mechanical testing program will employ multiple strain gage rosettes to determine the strains in the acetabular region of four normal hip joints during one-legged stance. After testing, the pelvis will be embedded in acrylic resin and sectioned. The global geometry will be determined. Each section will then be examined under reflected light microscopy and quantitative morphometric measurements of bone areal fraction and trabecular orientation will be mapped out for each section. Two 2-D and two 3-D finite element models (FEM's) will be constructed. The bone of the acetabular region will be modeled as a heterogeneous material. Material properties will be assigned to elements according to the morphometric parameters. The results of the FEM's will be compared to the mechanical testing data and the models will be refined in an iterative manner to ensure good correlation between the experimental and theoretical results. The experimentally verified FEM's of the acetabulum will then be used to calculate the deformations and stresses after total hip arthroplasty. Several different surgical techniques and prosthetic components will be evaluated. Important findings from FEM analysis of hip arthroplasty will then be experimentally verified with addition in vitro mechanical testing using strain rosettes.